i386 has show_trace_log_lvl and show_stack_log_lvl, allowing
traces to be emitted with log-level annotations. This patch
introduces them to x86_64, but log_lvl is only ever set to
an empty string. Output of traces is unchanged.

i386-chunk is whitespace-only.
Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>